In the US “sleet” is the term for a winter precipitation that occurs when snow falls through a layer of warm air and melts into water droplets, then re-freezes into ice pellets as it passes through colder air closer to the ground. In many other areas that were part of the British empire that precipitation is called “ice pellets” and “sleet” instead refers to a mix of snow and rain. In the US that’s called a “wintry mix.”
https://www.etymonline.com/word/sleet so not the version I grew up with.
Wintry mix, though, feels like a newer word to me. I don’t recall hearing it in the '80s, but maybe I just don’t remember it. Even the '90s, I’m not sure. Definitely at some point in the '00s, though.
Sleet to me (central Ohio, USA from birth until my mid-20s) is wind-driven chunks. It is not the same as “freezing rain” in any cases that I can think of, but there might be a small overlap on that venn diagram. I would say “wintry mix” these days, but I’m probably equally likely to say “a mix of snow and rain” or something.